U.S. patent number 8,414,679 [Application Number 12/851,892] was granted by the patent office on 2013-04-09 for producing an alloy with a powder metallurgical pre-material.
This patent grant is currently assigned to W. C. Heraeus GmbH. The grantee listed for this patent is Herwig Schiefer, Heiko Specht, Jens Troetzschel, Christoph Vogt. Invention is credited to Herwig Schiefer, Heiko Specht, Jens Troetzschel, Christoph Vogt.
United States Patent |
8,414,679 |
Schiefer , et al. |
April 9, 2013 |
Producing an alloy with a powder metallurgical pre-material
Abstract
One aspect is a method for producing an alloy, whereby the alloy
includes at least a first metal and a second metal, whereby firstly
a powder metallurgical route and subsequently a melt metallurgical
route is used sequentially in order to generate the alloy from the,
at least, first metal and the second metal. The method includes
grinding the first metal into a first metal powder, grinding the
second metal into a second metal powder, mixing the first metal
powder and the second metal powder to produce a blended powder,
generating a blended body from the blended powder by the powder
metallurgical route, and generating the alloy by melting the
blended body by the melt metallurgical route.
Inventors: |
Schiefer; Herwig (Frankfurt,
DE), Vogt; Christoph (St. Paul, MN), Specht;
Heiko (Hanau, DE), Troetzschel; Jens (Hanau,
DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Schiefer; Herwig
Vogt; Christoph
Specht; Heiko
Troetzschel; Jens |
Frankfurt
St. Paul
Hanau
Hanau |
N/A
MN
N/A
N/A |
DE
US
DE
DE |
|
|
Assignee: |
W. C. Heraeus GmbH (Hanau,
DE)
|
Family
ID: |
43448157 |
Appl.
No.: |
12/851,892 |
Filed: |
August 6, 2010 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20110033335 A1 |
Feb 10, 2011 |
|
Foreign Application Priority Data
|
|
|
|
|
Aug 6, 2009 [DE] |
|
|
10 2009 036 298 |
|
Current U.S.
Class: |
75/751; 75/770;
420/590; 419/33 |
Current CPC
Class: |
C22B
4/06 (20130101); B22F 9/04 (20130101); B22F
2998/10 (20130101); B22F 2009/041 (20130101); B22F
2998/10 (20130101); B22F 2009/041 (20130101); B22F
3/15 (20130101); C22B 9/00 (20130101) |
Current International
Class: |
C22C
1/02 (20060101); C22C 1/04 (20060101) |
Field of
Search: |
;75/770,751 ;420/590
;419/33 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
C 5588 VI |
|
Aug 1956 |
|
DE |
|
691 26 973 |
|
Nov 1991 |
|
DE |
|
0801138 |
|
Oct 1997 |
|
EP |
|
1444993 |
|
Nov 2004 |
|
EP |
|
59035642 |
|
Feb 1984 |
|
JP |
|
9118121 |
|
Nov 1991 |
|
WO |
|
2009079282 |
|
Jun 2009 |
|
WO |
|
Other References
"Periodic Table: Melting Point" at
http://www.chemicalelements.com/index.html. created by Yinon
Bentor. Copyright 1996-2009. Downloaded May 31, 2012. cited by
examiner .
English translation of JP 59-035642 by Fukazawa et al. published
Feb. 27, 1984. cited by examiner .
O'Brien, Barry et al., "Development of a New Niobium-Based Alloy
for Vascular Stent Applications," Journal of the Mechanical
Behavior of Biomedical Materials I, pp. 303-312 (2008). cited by
applicant .
The Restriction Requirement for U.S. Appl. No. 12/959,031 mailed
May 16, 2012 (6 pages). cited by applicant .
The Office Action for U.S. Appl. No. 12/959,031 mailed Jul. 17,
2012 (14 pages). cited by applicant.
|
Primary Examiner: Wyszomierski; George
Assistant Examiner: McGuthry Banks; Tima M
Attorney, Agent or Firm: Dicke, Billig & Czaja, PLLC
Claims
What is claimed is:
1. A method for producing an alloy, whereby the alloy includes at
least a first metal and a second metal, whereby firstly a powder
metallurgical route and subsequently a melt metallurgical route is
used sequentially in order to generate the alloy from the, at
least, first metal and the second metal, the method comprising:
grinding the first metal into a first metal powder; grinding the
second metal into a second metal powder; mixing the first metal
powder and the second metal powder to produce a blended powder;
generating a blended body from the blended powder by the powder
metallurgical route; and generating the alloy by melting the
blended body by the melt metallurgical route. characterized in that
inclusions of at least one of the first metal and the second metal
in the alloy are between 4 .mu.m and 20 nm in size.
2. The method according to claim 1, characterized in that the alloy
includes at least a third metal.
3. The method according to claim 2, characterized by: grinding the
third metal into a third metal powder; and mixing the third metal
powder with the blended powder.
4. The method according to claim 2, characterized by: grinding the
third metal into a third metal powder; generating an additional
body from the third metal powder by the powder metallurgical route;
and by the alloy being generated by parallel melting of the blended
body and the additional body by the melt metallurgical route.
5. The method according to claim 2, characterized by the alloy
being generated by parallel melting of the blended body and a body
made of the third metal by the melt metallurgical route.
6. The method according to claim 2, characterized in that the first
metal and/or the second metal have a higher melting temperature
than the third metal.
7. The method according to claim 2, characterized in that at least
one of the first metal, the second metal, and the third metal is
formed from a group consisting of the elements, Pt, Pd, Ag, Au, Nb,
Ta, Ti, Zr, W, V, Hf, Mo, Co, Cr, Ni, Ir, Re, and Ru.
8. The method according to claim 1, characterized in that melting
the alloy is performed multiple times.
9. The method according to claim 1, characterized in that the first
metal is ground into the first metal powder with a first powder
particle size of between 10 .mu.m and 0.1 .mu.m and/or the second
metal is ground into the second metal powder with a second powder
particle size of between 10 .mu.m and 0.1 .mu.m.
10. The method according to claim 1, characterized in that the
first metal and the second metal have different melting
temperatures.
11. A method for producing an alloy comprising: grinding a first
metal into a first metal powder; grinding a second metal into a
second metal powder; mixing the first metal powder and the second
metal powder to produce a blended powder; generating a blended body
from the blended powder by a powder metallurgical route; and
generating the alloy by melting the blended body by a melt
metallurgical route; characterized in that inclusions of at least
one of the first metal and the second metal in the alloy are
between 10 .mu.m and 10 nm in size.
12. The method according to claim 11, characterized in that the
powder metallurgical route comprises manufacturing a metal object
from a metal powder, and is a process from a group comprising hot
pressing, sintering, and hot isostatic pressing.
13. The method according to claim 11, characterized in that the
melt metallurgical route comprises manufacturing a metal object
that is melted by exposure to an energy source in a vacuum and is a
process from a group comprising vacuum induction, electron beam
melting, and arc melting.
14. The method according to claim 11, characterized in that the
alloy includes at least a third metal, and further comprising
grinding the third metal into a third metal powder, and mixing the
third metal powder with the blended powder.
15. The method according to claim 14, characterized in that at
least of the first metal, the second metal, and the third metal is
formed from a group consisting of the elements, Pt, Pd, Ag, Au, Nb,
Ta, Ti, Zr, W, V, Hf, Mo, Co, Cr, Ni, Ir, Re, and Ru.
16. The method according to claim 11, characterized in that the
first metal is ground into the first metal powder with a first
powder particle size of between 10 .mu.m and 0.1 .mu.m and/or the
second metal is ground into the second metal powder with a second
powder particle size of between 10 .mu.m and 0.1 .mu.m.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This Utility Patent Application claims priority to German Patent
Application No. DE 10 2009 036 298.3, filed on Aug. 6, 2009, which
is incorporated herein by reference.
BACKGROUND
One aspect relates to a method for producing an alloy.
Wires are needed in medical technology for producing medical
components. Said wires are made, for example, of alloys made of
multiple high-melting metals. In known production methods, rods
made of pure metal are bundled and melted in a high vacuum, for
example, by means of an electron beam. It has proven to be
disadvantageous that, in alloys that include metals such as
tantalum, niobium, and tungsten, the element with the highest
melting point is melted only incompletely. In some cases, larger
lumps, for example, tungsten, drop into the melt bath without
mixing with the other components of the alloy. Said non-melted
lumps of one of the alloy metals, called inclusions, later lead to
failure of the material when the alloy material is drawn out into a
wire. Fissures or cavities may thus form at the inclusions.
Moreover, the inclusions render the processing more difficult. The
inclusions reduce the fatigue resistance and lead to corrosion of a
wire made of said alloy.
For these and other reasons there is a need for the present
invention.
SUMMARY
One aspect is a method for producing an alloy. The alloy includes
at least a first metal and a second metal, and grinding the first
metal into a first metal powder and grinding the second metal into
a second metal powder. The first metal powder and the second metal
powder are mixed to produce a blended powder. A blended body is
generated from the blended powder by the powder metallurgical
route. The alloy is generated by melting the blended body by the
melt metallurgical route.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings are included to provide a further
understanding of embodiments and are incorporated in and constitute
a part of this specification. The drawings illustrate embodiments
and together with the description serve to explain principles of
embodiments. Other embodiments and many of the intended advantages
of embodiments will be readily appreciated as they become better
understood by reference to the following detailed description. The
elements of the drawings are not necessarily to scale relative to
each other. Like reference numerals designate corresponding similar
parts.
FIG. 1 illustrates a flow diagram of a method according to one
embodiment.
FIG. 2 illustrates a flow diagram of a first development of the
method according to one embodiment.
FIG. 3 illustrates another development of the method according to
one embodiment.
FIG. 4 illustrates a flow diagram of another embodiment of the
method according to one embodiment.
FIG. 5 illustrates a schematic view of a melt metallurgical
processing within the scope of the method according to one
embodiment.
DETAILED DESCRIPTION
In the following Detailed Description, reference is made to the
accompanying drawings, which form a part hereof, and in which is
shown by way of illustration specific embodiments in which the
invention may be practiced. In this regard, directional
terminology, such as "top," "bottom," "front," "back," "leading,"
"trailing," etc., is used with reference to the orientation of the
Figure(s) being described. Because components of embodiments can be
positioned in a number of different orientations, the directional
terminology is used for purposes of illustration and is in no way
limiting. It is to be understood that other embodiments may be
utilized and structural or logical changes may be made without
departing from the scope of the present invention. The following
detailed description, therefore, is not to be taken in a limiting
sense, and the scope of the present invention is defined by the
appended claims.
It is to be understood that the features of the various exemplary
embodiments described herein may be combined with each other,
unless specifically noted otherwise.
One aspect provides a method for producing an alloy, in which the
above-mentioned disadvantages are avoided, in particular to provide
a method that reduces the maximal size of the inclusions as
compared to known methods. Accordingly, one embodiment is a method
for producing an alloy and one embodiment is an alloy having
various features. In this context, any features and details that
are described in relation to the method shall also apply in
relation to the alloy and vice versa.
One aspect discloses a method for producing an alloy, whereby the
alloy includes at least a first metal and a second metal, whereby
firstly a powder metallurgical route and subsequently a melt
metallurgical route is used sequentially in order to generate the
alloy from the, at least, first metal and second metal, and the
method includes the steps of
a) grinding the first metal into a first metal powder;
b) grinding the second metal into a second metal powder;
c) mixing the first metal powder and the second metal powder to
produce a blended powder;
d) generating a blended body from the blended powder by the powder
metallurgical route;
e) generating the alloy by melting the blended body by the melt
metallurgical route.
One embodiment is based on combining two methods for producing an
alloy. This allows the advantages of the powder metallurgical route
and of the melt metallurgical route to be combined. Performing the
two routes--powder metallurgical and melt metallurgical--to be
illustrated in more detail below, sequentially results in alloys
whose inclusions are less than 10 .mu.m in size. In the context of
one embodiment, inclusion shall mean a region in the alloy that
includes only one of the various metals of the alloy. This
single-element region consists of only one metal of the alloy and
contacts the other metals of the alloy only on its outside
surfaces. The advantages of the powder metallurgical route in one
embodiment, is that it allows good homogenization and easy alloying
to be achieved at low sintering temperatures. In one embodiment,
these advantages are combined with the advantages of the melt
metallurgical route, that is, the high level of purity of the alloy
that can be achieved and the feasibility of alloying high-melting
metals together.
In the context of one embodiment, the term, "powder metallurgical
route", denotes a manufacturing process, in which a metal object is
manufactured from a metal powder. The term, "powder metallurgical
route", includes the following manufacturing processes: hot
pressing, sintering, hot isostatic pressing. Hot pressing involves
shaping and compacting a metal powder into a metal object by
exposure to a--in particular uniaxial--pressure and temperature.
Sintering involves a heat treatment, in which an object consisting
of metal powder is compacted. In hot isostatic pressing (HIP), a
metal powder that has been filled into a mold is compacted into a
metal object with approximately 100% density (isostatic) by means
of high pressure and high temperature.
Because of the high affinity for oxygen, it has proven to be
advantageous in one embodiment to melt refractory metals under
vacuum conditions. This allows pre-existing impurities to be
removed and gas inclusions in metals to be prevented. In the
context of one embodiment, the term, "melt metallurgical route",
means a manufacturing process, in which a metal object is melted by
exposure to an energy source in a vacuum. The term, "melt
metallurgical route", includes, for example, the following
manufacturing processes: vacuum induction, electron beam melting,
and arc melting. In vacuum induction, the metal object to be melted
is melted in a crucible by means of induction under vacuum
conditions and then poured into a water-cooled crucible. In
electron beam melting, energy-rich electron beams are used under
vacuum conditions to melt high-melting materials, which are then
poured into an ingot mold with a floor, which can be lowered, and
cooled walls. In arc melting, an arc is ignited between the metal
object to be melted and an electrode by means of a high voltage and
under vacuum conditions, which causes the material to melt.
One embodiment of one method is characterized in that the alloy
includes at least a third metal. Alloys that are used in the area
of medical technology are often generated from high-melting metals.
Alloys of this type commonly include more than only two metals. The
method according to one embodiment has proven to be well-suited for
producing a tantalum-niobium-tungsten alloy (TaNbW alloy containing
10 wt. % Nb and 7.5 wt. % W). With regard to the nomenclature of
the patent claim, tungsten therein functions as first metal,
tantalum as second metal, and niobium as third metal. In this
context, tantalum and tungsten are generated as a pre-alloy by the
powder metallurgical and melt metallurgical routes. The third
metal--in general residues of tantalum and niobium--is added to the
two first metals according to the procedural steps to be described
below.
One development of the method according to one embodiment is
characterized by i. grinding the third metal into a third metal
powder; and ii. mixing the third metal powder with the blended
powder in step c).
In this embodiment of the method, the third metal is ground into a
third metal powder. The first, second, and third metal powder are
mixed to form a blended powder, in which the weight fractions of
the three metal powders correspond to the alloying ratio desired
later on. This embodiment of the method is advantageous in that it
is easy to perform. All it requires is grinding the three metal
powders. In the process, the size of the metal powder into which
the metal is ground determines the size of the inclusions in the
finished alloy. The grinding size that has proven to be
advantageous in one embodiment is illustrated in more detail
below.
Another development of the method according to one embodiment is
characterized by i. grinding the third metal into a third metal
powder; ii. generating an additional body from the third metal
powder by the powder metallurgical route;
and by the alloy being generated in step e) by parallel melting of
the blended body and the additional body by the melt metallurgical
route. As before, in this embodiment of the method, the third metal
is ground into a metal powder. Deviating from the embodiment
described above, the third metal powder is not admixed to the
blended powder, though. Rather, an additional body is generated
from the third metal powder by the powder metallurgical route.
Accordingly, for example, the third metal powder can be pressed to
form the additional body and hardened by a heat treatment. In the
subsequent step e), the blended body made of the first two metals
and the additional body are then melted jointly by the melt
metallurgical route. This can be effected, for example, by
bombardment with electrons in electron beam melting. In the
process, the melted particles of the blended body and the
additional body flow into a water-cooled ingot mold and solidify
therein as an alloy. In this embodiment of the melt metallurgical
route, the blended body and the additional body are arranged next
to each other such that both are hit by the electron beam and are
thus melted in parallel. Said parallel performance of the melt
metallurgical route ensures that melted particles of all three
metals flow into the ingot mold and solidify therein as a
homogeneous alloy whose inclusions are less than 10 .mu.m in size.
Said alloys can then be used for medically implantable devices. In
the scope of the variant of the method according to one embodiment
described here, the third metal powder can just as well be
compacted by hot isostatic pressing (HIP). Subsequently, the HIP
body is cut into oblong bars which are melted jointly with the
blended body and combined into an alloy by the melt metallurgical
route.
Another development of the method according to one embodiment is
characterized in that the alloy is generated in step e) by means of
parallel melting of the blended body and a body made of the third
metal by the melt metallurgical route. In the scope of said
embodiment of the method, the third metal is subjected neither to
powder metallurgical, nor to melt metallurgical pre-processing.
Rather, a body made of the third metal is processed together with
the blended body by the melt metallurgical route. There is no
processing of the body made of the third metal involved before it
is melted by the melt metallurgical route. The body made of the
third metal can be a bar or a rod that includes the third metal in
pure form. Said body is bundled with the blended body at a ratio
that corresponds to the later ratio of the metals in the alloy.
Thereafter follows the melting of the body and blended body by the
melt metallurgical route.
In order to attain particular purity of the alloy and to further
reduce the size of any inclusions, it has proven to be advantageous
in one embodiment to supplement the method in that the method
includes after step d) the step of
f) melting the alloy by the melt metallurgical route.
In the scope of procedural step f), the alloy generated in step e)
is melted again. After the alloy generated in step e) has
solidified, it can be melted again by the melt metallurgical route.
Accordingly, it is conceivable, for example, to melt the alloy from
step e) in a vacuum using an electron beam. Any inclusions, which
already are less than 10 .mu.m in size, can be further reduced in
size by the repeated melting. A further advantageous development of
said embodiment provides for step f) to be performed multiply.
Accordingly, it has proven to be advantageous in one embodiment to
perform step f) two to ten times, in particular three to five
times. Repeated melting of the alloy by the melt metallurgical
route further reduces the size of the inclusions. Accordingly, it
was possible to realize inclusion sizes between 4 .mu.m and 10 nm
in particular by means of melting three to five times in the scope
of step f). Alloys with inclusions of this size can be used, in
particular, for medically implantable objects to particular
advantage in some embodiments. Inclusions of this size do not
reduce the fatigue resistance of the finished product.
Another development of the method according to one embodiment is
characterized in that the first metal is ground into a first metal
powder with a first powder particle size of between 10 .mu.m and
0.1 .mu.m and/or the second metal is ground into a second metal
powder with a second powder particle size of between 10 .mu.m and
0.1 .mu.m. The first and the second metal each are ground into
metal powder according to the method. Depending on the development
of one embodiment, the third metal also can be ground into a third
metal powder. In order to ensure that the inclusions, that is,
those regions inside the alloy, in which only a single metal is
present in elemental form, are small in size, the metals must be
ground fine enough during the preparation phase for the powder
particle size of the individual metal powders to be between 10
.mu.m and 0.1 .mu.m, since the size of the powder particles is
correlated to the size of the inclusions. In the context of one
embodiment, the term, "powder particle size", is used to refer to
the maximal size of those particles of the metal powder that is
achieved within the scope of grinding and ensuing screening.
Accordingly, the size of the mesh of the sieve used to screen the
metal powder after grinding indicates the upper limit of the powder
particle size. According to one embodiment, the required powder
particle size shall specify the maximal size of a particle of the
metal powder. No particle of the metal powder shall be of a size
larger than the powder particle size, but can be of any smaller
size.
Due to the grinding of the first metal and second metal, and in one
embodiment, of the third metal also, the size of the inclusions of
the first and/or second and/or third metal in the alloy is between
10 .mu.m and 10 nm. If, in addition, step f) according to one
embodiment is performed multiply, it is feasible according to one
embodiment for the size of the inclusions to be between 4 .mu.m and
20 nm. Said size is non-objectionable for the use in alloys of
medically implantable devices.
Another development of the method according to one embodiment is
characterized in that the first metal and the second metal have
different melting temperatures, in particular in that the first
metal and/or the second metal have a higher melting temperature
than the third metal. Especially in the case of high-melting
metals, in particular refractory metals, the disadvantages
specified above can occur during known melting methods. Since
metals of this type are used in medicine due to their good
biocompatibility, the method according to one embodiment lends
itself to the production of alloys for medical instruments and
objects. In this context, it is advantageous in one embodiment for
the first metal and/or the second metal and/or the third metal to
be formed from the group consisting of the elements, Pt, Pd, Ag,
Au, Nb, Ta, Ti, Zr, W, V, Hf, Mo, Co, Cr, Ni, Ir, Re, Ru.
The scope of one embodiment also includes disclosure of an alloy
made of at least a first metal and a second metal, characterized in
that the alloy is generated according to any one of the methods
described above.
The technical issue, on which the method according to one
embodiment for producing an alloy is based, is that not all metals
are distributed homogeneously in the finished alloy, in particular
in the case of high-melting refractory metals, but rather
regions--also called inclusions--are formed, in each of which only
one metal of the various metals used for the alloy is present in
pure form. Inclusions of this type can significantly reduce the
fatigue resistance of the finished product. In order to overcome
this disadvantage, one embodiment discloses a method for producing
an alloy, in one embodiment, made of refractory metals, whereby the
alloy 100 includes at least a first metal 10 and a second metal 20.
In this context, alloy 100 shall be understood to be a fusion of
said two metals 10, 20 into a combination metal. The special
feature according to one embodiment is that first a powder
metallurgical route and subsequently a melt metallurgical route are
used sequentially, that is, one after the other, for producing the
alloy.
FIG. 1 illustrates a flow diagram of the method according to one
embodiment for producing the alloy 100. The method is based on the
use of the first metal 10 and the second metal 20. Firstly, the
first metal 10 is ground into a first metal powder 11. In parallel
or subsequently, the second metal 20 is ground into a second metal
powder 21. In this context, it has proven to be advantageous in one
embodiment for the first metal 10 to be ground into a first metal
powder 11 with a particle size of between 10 .mu.m and 0.1 .mu.m.
The same applies to the second metal that is ground into a second
metal powder 21. Subsequently, the first metal powder 11 and the
second metal powder 21 are mixed to form a blended powder 40. Said
blended powder 40 includes the first metal powder 11 and the second
metal powder 21 in a distribution that corresponds to the one which
the two metals 10, 20 are to possess later in the alloy 100. The
blended powder 40 is used to generate a blended body 45 by the
powder metallurgical route 50. The powder metallurgical route 50
can, for example, be a process of hot isostatic pressing (HIP). In
the process, the blended powder 40 is compacted into the blended
body 45 by the influence of pressure and heat. Subsequently, the
blended body 45 can be cut into oblong bars, which are then melted
by the melt metallurgical route 60 in order to form the alloy
100.
In the context of one embodiment, the powder metallurgical route,
in particular, refers to the manufacturing of a product using the
following steps, whereby each step can take a different form:
1) generation of a metal powder 11, 21,
2) shaping, and
3) heat treatment.
For manufacturing an alloy 100 by means of the powder metallurgical
route 50, metal powders 10, 20 of pure metals or alloys in powder
particle sizes are needed. The type of powder production has a
major impact on the properties of the powders. Mechanical methods,
chemical reduction methods or electrolytic methods as well as the
carbonyl method, spinning, atomizing, and other methods can be used
for producing the powder. The shaping involves compaction of the
metal powder in pressing tools under high pressure (between 1 and
10 t/cm.sup.2 (tonnes per square centimeter) to form green
compacts. Other possible methods include compaction by vibration,
slip casting method, and methods involving the addition of binding
agents. In heat treatment (also called sintering), the powder
particles are solidly connected at their contact surfaces by
diffusion of the metal atoms. The sintering temperature of
single-phase powders is between 65 and 80% of the solidus
temperature.
In another development, the alloy includes at least a third metal
30. In order to integrate said third metal into the alloy such that
as little inclusions as possible form, the method according to one
embodiment can be supplemented by further procedural steps. The
sequence thereof is illustrated in FIGS. 2 to 4.
FIG. 2 illustrates a method according to one embodiment.
Paralleling the grinding of the first metal 10 and second metal 20,
the third metal 30 is ground into a third metal powder 31. Said
third metal powder 31 is eventually introduced into the blended
powder 40'. Accordingly, the three metals 10, 20, 30 are present in
the metal powder 40' in the form of powders and in weight ratios as
are desired to be present later in the alloy 100. The subsequent
steps correspond to those procedural steps that were also
illustrated in FIG. 1. Accordingly, a blended body 45 is generated
from the blended powder 40' by the powder metallurgical route 50.
Said blended body 45 is then melted by the melt metallurgical route
in order to obtain the alloy 100.
Alternatively, the third metal 30 can be introduced into the alloy
100 by a different route, such as is illustrated in FIG. 3.
Although the third metal 30 is ground into a metal powder 31 herein
as well, said third metal powder 31 is not added to the blended
powder 40'. Rather, the third metal powder 31 is used to generate
an additional body 32 by the powder metallurgical route. Said
additional body 32 can be generated, for example, by hot isostatic
pressing, and subsequently be shaped into an oblong bar.
Subsequently, the blended body 45 and the additional body 32 are
melted in parallel by the melt metallurgical route 60. By jointly
embarking on the melt metallurgical route 60, the alloy 100 is
produced from the blended body 45 and the additional body 32.
In another alternative development of the method according to one
embodiment, the third metal 30, in one embodiment in pure form, is
provided in the form of a body 33. Said body 33 can, for example,
be a bar made of the third metal 30. Said bar is melted jointly
with the blended body 45, which was generated by the powder
metallurgical route, using the melt metallurgical route 60. Thus a
joint alloy 100 is formed. The individual procedural steps are
illustrated in FIG. 4.
FIG. 5 illustrates the melt metallurgical route 60 by means of an
electron beam melting process. As explained above, the third metal
30 can be ground into a third metal powder 31 and an additional
body 32 can be generated by the powder metallurgical route 50.
Subsequently, said additional body 32 is spatially arranged next to
the blended body 45 in a vacuum chamber. An electron beam source 70
generates an electron beam 71 that knocks individual metal
particles out of the blended body 45 or the additional body 32.
Said metal particles surprisingly are of a size that is identical
to a powder particle size of the corresponding metal powder, 11,
21, 31 of the available metals 10, 20, 30, respectively.
Accordingly, the first metal 10 and second metal 20 should be
ground to a powder particle size of between 10 .mu.m and 0.1 .mu.m
in order for inclusions of the first metal 10 and/or the second
metal 20 in the alloy 100 to be between 10 .mu.m and 10 nm in size.
The melted metal particles flow into the ingot mold 110 and form
the alloy 100 therein. For the alloy 100 to solidify readily, the
walls 117 of the ingot mold are cooled. A floor 115 that can be
lowered ensures that the path to be traveled by the melted metal
particles until they hit the surface of alloy 100 is always the
same.
A development of the method according to one embodiment provides
the alloy 100 to be melted again subsequent to step d) by the melt
metallurgical route 60. Multiple melting of the alloy 100 by the
melt metallurgical route 60 allows the size of the inclusions of
the first metal 10 and/or the second metal 20 and/or the third
metal 30 in the alloy to be reduced further. It has proven to be
advantageous in one embodiment to melt the generated alloy three to
five times by melt metallurgical means. In the process, it is
feasible to attain inclusions of the first metal 10 and/or the
second metal 20 and/or the third metal 30 whose size is between 4
.mu.m and 20 nm. Inclusions of this type no longer have an impact
on the fatigue resistance of the alloy in implantable medical
devices.
Although specific embodiments have been illustrated and described
herein, it will be appreciated by those of ordinary skill in the
art that a variety of alternate and/or equivalent implementations
may be substituted for the specific embodiments shown and described
without departing from the scope of the present invention. This
application is intended to cover any adaptations or variations of
the specific embodiments discussed herein. Therefore, it is
intended that this invention be limited only by the claims and the
equivalents thereof.
* * * * *
References